Method of controlling a laser bond inspection system

ABSTRACT

A method of laser bond inspection is provided. The method includes applying a thermochromatic energy-absorbing material to an inspection site of a test article. The method includes delivering a first amount of energy to the inspection site using a laser. The first amount of energy generates stresses in the test article. The method includes absorbing the first amount of energy into the thermochromatic energy-absorbing material to produce an observable thermal response that correlates to the first amount of energy.

BACKGROUND

The field of the disclosure relates generally to laser inspection and,more specifically, to laser bond inspection device and a method of laserbond inspection.

In certain areas of manufacturing, two components are bonded together toform a bonded structure. Manufacturers of such bonded structures inspectthe quality of the bond through various destructive and non-destructivetesting. One type of non-destructive testing is laser bond inspection,where a laser is used to pass energy into an overlay to generate acalibrated compression wave that propagates through a structure. Thereflection of the calibrated compression wave generates a tensile wavethat stresses the bond as the tensile wave propagates back through thestructure.

BRIEF DESCRIPTION

According to one aspect of the present disclosure, a method of laserbond inspection is provided. The method includes applying athermochromatic energy-absorbing material to an inspection site of atest article. The method includes delivering a first amount of energy tothe inspection site using a laser. The first amount of energy generatesstresses in the test article. The method includes absorbing the firstamount of energy into the thermochromatic energy-absorbing material toproduce an observable thermal response that correlates to the firstamount of energy.

According to another aspect of the present disclosure, a method ofcontrolling a laser bond inspection device (LBID) is provided. Themethod includes setting an energy output level for a laser of the LBIDto a target amount of energy. The method includes engaging the laser todeliver a first amount of energy to an inspection site on a testarticle. A thermochromatic energy-absorbing material is applied to theinspection site. The method includes verifying, based on an observablethermal response of the thermochromatic energy-absorbing material to thefirst amount of energy, the target amount of energy was delivered to theinspection site.

According to yet another aspect of the present disclosure, a laser bondinspection system is provided. The laser bond inspection system includesa laser, a thermochromatic energy-absorbing material, and a camera. Thelaser is configured to deliver a first amount of energy to an inspectionsite of a test article. The thermochromatic energy-absorbing material isapplied to the inspection site and is configured to absorb the firstamount of energy. The thermochromatic energy-absorbing material isconfigured to generate stresses within the test article. Thethermochromatic energy-absorbing material is configured to exhibit anobservable thermal response to the first amount of energy. The camera isconfigured to capture the observable thermal response.

The features, functions, and advantages that have been discussed can beachieved independently in various embodiments or may be combined in yetother embodiments further details of which can be seen with reference tothe following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is diagram of one embodiment of a laser bond inspection system;

FIG. 2 is a cross-sectional diagram of the laser bond inspection systemshown in FIG. 1;

FIG. 3 is a cross-sectional diagram of one embodiment of athermochromatic energy-absorbing material;

FIG. 4 is a flow diagram of one embodiment of a method of laser bondinspection; and

FIG. 5 is a flow diagram of one embodiment of a method of controlling alaser bond inspection device.

DETAILED DESCRIPTION

As used herein, an element or step recited in the singular and proceededwith the word “a” or “an” should be understood as not excluding pluralelements or steps unless such exclusion is explicitly recited.Furthermore, references to “one embodiment” of the present invention orthe “exemplary embodiment” are not intended to be interpreted asexcluding the existence of additional embodiments that also incorporatethe recited features.

During manufacturing, two components are joined with a bond having anintended level of strength. During laser bond inspection, a calibratedamount of energy is used to generate stress in the bond. A good bond isunaffected by the stress, while a bad bond fails. Failure of a bond maybe visually detectable or, in certain applications, by ultrasonictesting.

An important aspect of laser bond inspection is the ability to deliver acalibrated amount of energy to an energy absorbing overlay using thelaser. Too little energy may not adequately test the bond, and too muchenergy may destroy a good bond. It is realized herein applying athermochromatic material to an energy absorbing overlay at a laser bondinspection site on a test article provides immediate indication ofenergy transfer into the energy absorbing overlay and the test article.The thermochromatic material exhibits a thermal response to the energytransfer from the laser by changing color and intensity. The thermalresponse is observable under a selected wavelength of light, such as,for example, ultraviolet (UV) light. For example, the thermal responsemay be captured using a charge coupled device (CCD) or CMOS type cameraunder UV light. In certain embodiments, the thermal response isobservable visually by a user of the laser bond inspection system in thenormal human-visible spectrum. The thermal response produces a spectrumof colors corresponding to a range of energy absorbed. For a particularbond to be tested using a particular amount of energy, the appropriateamount of energy transfer from the laser to the energy absorbing overlayis verified by comparing the resulting color change of thethermochromatic material with an expected color in the spectrum.Similarly, too little or too much energy transfer produces distinctcolors in the spectrum.

FIG. 1 is block diagram of a laser bond inspection system 100. Laserbond inspection system 100 includes a laser bond inspection device 110configured to generate a laser beam 120. Laser bond inspection system100 also includes a thermochromatic energy-absorbing material 130applied to an inspection site of a test article 140. Test article 140includes a first component 150 and a second component 160 joined by abond 170. Thermochromatic energy-absorbing material 130 may include ahomogeneously thermochromatic material. In alternative embodiments,thermochromatic energy-absorbing material 130 may include anenergy-absorbing material coated with a thermochromatic material, suchthat the coating layer is thermochromatic, but the energy-absorbingmaterial is not.

During operation, LBID 110 generates and directs laser beam 120 towardtest article 140. Laser beam 120 is configured to deliver a calibratedamount of energy to the inspection site. The calibrated amount of energyvaries for each test article. For test article 140, a target amount ofenergy is computed that will produce a target amount of stress in testarticle 140 to test bond 170. The amount of energy actually delivered bylaser beam 120 may vary during operation of LBID 110.

The energy delivered by laser beam 120 is absorbed by thermochromaticenergy-absorbing material 130. The absorbed energy creates a compressionwave 180 that propagates through test article 140. When compression wave180 reaches the rear face of test article 140, it is reflected backtoward thermochromatic energy-absorbing material 130 as a tensile wave190. Tensile wave 190 stresses bond 170. The target amount of energy isdetermined such that tensile wave 190 delivers the target amount ofstress in test article 140. If too little energy is absorbed, from laserbeam 120, into thermochromatic energy-absorbing material 130, the amountof stress generated by tensile wave 190 will not be sufficient toproperly test bond 170. If too much energy is absorbed intothermochromatic energy-absorbing material 130, from laser beam 120, theamount of stress generated by tensile wave 190 may exceed the strengthof a good bond, thus damaging an otherwise good bond.

Thermochromatic energy-absorbing material 130 is configured to exhibitan observable thermal response to the energy delivered by laser beam 120and absorbed into thermochromatic energy-absorbing material 130. Theobservable thermal response includes, for example, color change andintensity change. The target amount of energy for test article 140causes an expected thermal response in thermochromatic energy-absorbingmaterial 130 that correlates to the target amount of energy. Theexpected thermal response may include, for example, a specific color andintensity. If laser beam 120 delivers too little energy tothermochromatic energy-absorbing material 130, a distinct thermalresponse is exhibited, the distinct thermal response correlating to theactual amount of energy absorbed. If laser beam 120 delivers too muchenergy to thermochromatic energy-absorbing material 130, anotherdistinct thermal response is exhibited and correlates to the actualamount of energy absorbed.

FIG. 2 is a cross-sectional diagram of the laser bond inspection system100 shown in FIG. 1. LBID 110 includes a laser source 210 configured togenerate a laser beam 220. LBID 110 includes a vacuum chamber 230 that,when joined with thermochromatic energy-absorbing material 130, isconfigured to generate a vacuum within which laser beam 220 propagates.A layer of water 240 is disposed within vacuum chamber 230 atthermochromatic energy-absorbing material 130 to contain pressurebuildup at the inspection site of test article 140.

LBID 110 further includes a camera 250 configured to capture theobservable thermal response exhibited by thermochromaticenergy-absorbing material 130 during operation. In certain embodiments,camera 250 includes a charge coupled device. In alternative embodiments,camera 250 may include an infrared camera or an optical camera. Incertain embodiments, LBID 110 includes an ultraviolet (UV) light sourcefor illuminating the inspection site while camera 250 captures theobservable thermal response.

In certain embodiments, laser bond inspection system 100 includes acontroller 260 configured to receive images from camera 250. Controller260 is further configured to process an image of the observable thermalresponse to determine a difference between the energy absorbed intothermochromatic energy-absorbing material 130 and the target amount ofenergy. In certain embodiments, controller 260 is configured to computea chromatic value for the energy absorbed that is compared to apredetermined chromatic value for the target amount of energy.Controller 260 is configured to adjust laser source 210 to deliver asecond amount of energy to compensate for the determined differencebetween the target amount of energy and the first amount of energyactually delivered. For example, controller 260 increases the energylevel of laser beam 220 if the first amount of energy delivered is lessthan the target amount of energy. Conversely, controller 260 decreasesthe energy level of laser beam 220 if the first amount of energydelivered is greater than the target amount of energy.

FIG. 3 is a cross-sectional diagram of thermochromatic energy-absorbingmaterial 130 shown in FIGS. 1 and 2. Thermochromatic energy-absorbingmaterial 130 includes an energy absorbing overlay 310. Energy absorbingoverlay 310 includes a first surface having an adhesive layer 320 thatfacilitates adhesively coupling energy absorbing overlay 310 to a testarticle, such as test article 140 shown in FIGS. 1 and 2. Energyabsorbing overlay 310 includes a second surface opposite the firstsurface. The second surface has a thermochromatic material 330 appliedsuch that energy absorbed into energy absorbing overlay 310 generates anobservable thermal response in thermochromatic material 330.

In certain embodiments, for example, energy absorbing overlay 310 ismanufactured as a roll of tape that can be applied along bond lines invarious test articles.

In alternative embodiments, energy absorbing overlay 310 hasthermochromatic properties such that energy-absorbing material 130 ishomogeneously thermochromatic, with the exception of adhesive layer 320.In such a material, thermochromatic material 330 is omitted, as energyabsorbing overlay 310 has the desired thermochromatic properties.

FIG. 4 is a flow diagram of one embodiment of a method 400 of laser bondinspection of a test article. Method 400 includes a start step 410. At apreparation step 420, a thermochromatic energy-absorbing material isapplied to an inspection site of the test article. In certainembodiments, applying the thermochromatic energy-absorbing materialincludes applying a thermochromatic energy-absorbing tape over a bondline of the test article.

At a delivery step 430, a first amount of energy is delivered to theinspection site using a laser. The first amount of energy generatesstresses in the test article. In certain embodiments, method 400includes a computing step where a target amount of energy to bedelivered is computed based on a target amount of stress to be appliedto the test article.

At an absorbing step 440, the first amount of energy is absorbed intothe thermochromatic energy-absorbing material to produce an observablethermal response that correlates to the first amount of energy. Theobservable thermal response facilitates immediate feedback of the amountof energy delivered by the laser.

In certain embodiments, method 400 includes a capture step during whichthe observable thermal response is captured and analyzed. Based on acaptured observable thermal response, the laser bond inspection systemdetermines whether the first amount of energy is less than or greaterthan the target amount of energy. The captured observable thermalresponse is compared to an expected thermal response correlating to thetarget amount of energy. In certain embodiments, the observable thermalresponse is quantifiable as a chromatic value correlating to the firstamount of energy absorbed. If, for example, the first amount of energydelivered is less than the target amount of energy, a second amount ofenergy is computed that is greater than the first amount of energy. Thesecond amount of energy is then delivered to a second inspection site.The process can be repeated as necessary until the test article issufficiently tested.

In certain embodiments, capturing the observable thermal response iscarried out using a camera. In certain embodiments, the inspection siteis illuminated by a UV light source to facilitate capture of theobservable thermal response. An image of the observable thermal responsecaptured by the camera is then processed. In certain embodiments, theimage is processed to determine a chromatic value for the observablethermal response that is compared to a chromatic value for the targetamount of energy.

In certain embodiments, a user observes the thermal response or theimage of the thermal response to determine whether the target amount ofenergy was delivered.

In certain embodiments, method 400 includes a calibration step beforepreparation step 420. During the calibration step, the thermochromaticenergy-absorbing material is applied to a calibration article. The laseris then used to deliver the target amount of energy to thethermochromatic energy-absorbing material on the calibration article toverify the laser is delivering the appropriate amount of energy andproducing the expected thermal response in the thermochromaticenergy-absorbing material prior to inspecting the test article. Incertain embodiments, the calibration step is repeated periodically tore-verify the energy output of the laser.

The method ends at an end step 450.

FIG. 5 is a flow diagram of one embodiment of a method 500 ofcontrolling a laser bond inspection device (LBID). The method begins ata start step 510. At a setup step 520, an energy output level for alaser of the LBID is set to a target amount of energy. At a deliverystep 530, the laser is engaged to deliver a first amount of energy to aninspection site of a test article. The test article has athermochromatic energy-absorbing material applied at the inspectionsite. The thermochromatic energy-absorbing material is configured toabsorb the first amount of energy delivered by the laser. Thethermochromatic energy-absorbing material is further configured toexhibit an observable thermal response to the first amount of energyabsorbed.

At a verification step 540, the LBID verifies the target amount ofenergy was delivered to the inspection site based on the observablethermal response exhibited by the thermochromatic energy-absorbingmaterial to the first amount of energy. If the first amount of energy isequal to or within a range of the target amount of energy, theobservable thermal response will match an expected thermal response forthe target amount of energy. If the observable thermal responseindicates less than the target amount of energy was delivered to theinspection site, the energy output level for the laser is increased. Ifthe observable thermal response indicates greater than the target amountof energy was delivered to the inspection site, the energy output levelfor the laser is decreased.

In certain embodiments, the observable thermal response is measured, orquantified for comparison to the expected thermal response. Such ameasurement may be made manually by a user, or may be captured andcomputed using a camera, spectrophotometer, or other instrument. Incertain embodiments, method 500 includes a feedback step where theobserved thermal response is used to adjust a fluence of the laser.

In certain embodiments, verification step 540 includes capturing theobservable thermal response of the thermochromatic energy-absorbingmaterial to the first amount of energy. Once captured, the observablethermal response is compared to the expected thermal response for thetarget amount of energy. In certain embodiments, comparing theobservable thermal response to the expected thermal response includescomputing a first chromatic value for the observable thermal responseand comparing the first chromatic value to a second chromatic value forthe expected thermal response and correlating to the target amount ofenergy.

The method ends at an end step 550.

This written description uses examples to disclose various embodiments,which include the best mode, to enable any person skilled in the art topractice those embodiments, including making and using any devices orsystems and performing any incorporated methods. The patentable scope isdefined by the claims, and may include other examples that occur tothose skilled in the art. Such other examples are intended to be withinthe scope of the claims if they have structural elements that do notdiffer from the literal language of the claims, or if they includeequivalent structural elements with insubstantial differences from theliteral languages of the claims.

What is claimed is:
 1. A method of controlling a laser bond inspectiondevice (LBID) having a laser and a camera, the method comprising:setting an energy output level for the laser of the LBID to a targetamount of energy; engaging the laser to deliver a first amount of energyto an inspection site on a test article, the inspection site having athermochromatic energy-absorbing material applied thereto; observing,using the camera, an observable thermal response of the thermochromaticenergy-absorbing material to the first amount of energy; and verifying,based on the observable thermal response, the target amount of energywas delivered to the inspection site.
 2. The method of claim 1 furthercomprising increasing the energy output level for the laser if theobservable thermal response indicates less than the target amount ofenergy was delivered to the inspection site.
 3. The method of claim 1further comprising decreasing the energy output level for the laser ifthe observable thermal response indicates more than the target amount ofenergy was delivered to the inspection site.
 4. The method of claim 1,wherein verifying the target amount of energy was delivered to theinspection site comprises: capturing the observable thermal response ofthe thermochromatic energy-absorbing material to the first amount ofenergy; and comparing the observable thermal response to an expectedthermal response correlating to the target amount of energy.
 5. Themethod of claim 4, wherein comparing the observable thermal response tothe expected thermal response comprises: computing a first chromaticvalue of the observable thermal response; and comparing the firstchromatic value to a second chromatic value correlating to the targetamount of energy.
 6. The method of claim 1 further comprising computingthe target amount of energy to be delivered based on a target amount ofstress to be applied to the inspection site.
 7. The method of claim 6,wherein observing comprises capturing the observable thermal responseand verifying comprises determining the first amount of energy is lessthan the target amount of energy based on comparing the observablethermal response to an expected thermal response correlating to thetarget amount of energy.
 8. The method of claim 7 further comprising:computing a second amount of energy to be delivered, wherein the secondamount of energy is greater than the first amount of energy; anddelivering the second amount of energy to a second inspection site usingthe laser.
 9. The method of claim 6, wherein capturing the observablethermal response comprises capturing the observable thermal responseusing the camera.
 10. The method of claim 1, wherein observing theobservable thermal response comprises capturing the observable thermalresponse using the camera.
 11. The method of claim 10, wherein capturingthe observable thermal response further comprises illuminating theinspection site using an ultraviolet (UV) light source for capture bythe camera.
 12. The method of claim 10 further comprising computing achromatic value correlating to the first amount of energy based on theobservable thermal response captured in an image by the camera.
 13. Themethod of claim 10, wherein using the camera comprises using a chargecoupled device.
 14. The method of claim 10 further comprising receivingan image of the observable thermal response captured by the camera at acontroller.
 15. The method of claim 14 further comprising processing theimage, at the controller, to determine a difference between the firstamount of energy absorbed into the thermochromatic energy-absorbingmaterial and the target amount of energy.
 16. The method of claim 15further comprising computing, at the controller, a second amount ofenergy to compensate for the difference.
 17. The method of claim 16further comprising adjusting the laser to deliver the second amount ofenergy.
 18. The method of claim 1 further comprising generating a vacuumwithin a vacuum chamber within which the first amount of energy is to bedelivered to and absorbed by the thermochromatic energy-absorbingmaterial.